1. Field of the Invention
This invention relates to chemical vapor deposition (CVD) of group IB metals, and specifically Cu, Ag, and Au, and more particularly to an improved CVD method wherein films of very high quality can be formed at low temperatures, using either thermal or radiation beam-induced CVD.
2. Description of the Related Art
The deposition of metals from the vapor phase is important in many industries, and in particular in the electronics industry. In this industry, metallic depositions are often undertaken, involving metals such as copper, silver, gold, tungsten, etc. In particular, these metals are often used for interconnection lines and in packaging for semiconductor chips, circuits, and packages. Another application of these metals is their deposition into vias, trenches, and other recesses or stepped structures. Such requirements and uses are apparent in the semiconductor industry and in packaging where multilevel interconnections through openings in insulating layers have to be provided.
In the environment of microelectronic circuitry and packaging, it is often the situation that low temperature processes are required in order to preserve the necessary characteristics of underlying layers. For example, most photosensitive resists cannot be subjected to temperatures above about 175.degree. C. without losing their ability to be exposed, developed, and patterned. As another example, most polymer layers, such as polyimide, require processing temperatures less than the glass transition temperature of the polymer in order to maintain the desired properties of the polymer. Thus, it is important to provide a technique for depositing metal lines at temperatures which are sufficiently low that the technique can be used in the presence of other layers having temperature-sensitive properties.
In the microelectronics industry, as well as in other industries, it is also the situation that the deposition must occur onto substrates which have irregular topography. For example, in semiconductor structures, interconnection lines must often be provided over nonplanar surfaces, including those having steps defining an irregular surface. A technique providing conformal deposition, i.e., deposition of continuous layers over irregular substrates, is a necessity. In this type of an environment where conformal deposition is required, techniques such as evaporation and sputtering (which are line-of-sight techniques) cannot be used. For this purpose, CVD techniques are preferred. However, CVD of metals, while being generally known, has not been extensively practiced due to the following reasons, among others: poor film quality, requirement of high processing temperatures; incorporation of impurities and other defects in the deposited film; the inability to transport vapors of the metal complex without decomposition of the vapors, and the instability of the precursors used in the deposition systems. Most generally, it is desired to deposit films having excellent electrical conductivity, which means that the films must have minimal carbon and oxygen contamination. Presently known CVD techniques have not been successful, particularly with respect to providing films of very high quality.
Both thermal and laser-induced deposition of metals from the gas phase has been attempted in the art. Published studies have generally described metals and elements whose volatile precursors are readily available from commercial sources, usually metal alkyls or metal carbonyls. For example, chromium has been deposited from chromium carbonyl and cadmium has been deposited from dimethyl cadmium. These materials, and others, have been used for maskless writing of metals, microelectronic circuit fabrication, metal line repair, and metal mask repair.
A metal of considerable importance and one which has not heretofore been successfully deposited by CVD is copper. One reason may be the lack of a suitable precursor since copper carbonyl does not exist for practical purposes and copper alkyls are polymeric and nonvolatile. F. A. Houle et al, Appl. Phys. Lett. 46 (2), 15, Jan. 1985, at page 204 describes laser-induced CVD of copper using a volatile copper coordination complex. The precursor was bis-(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate) copper (II), CuHF. This same compound was also used to make copper films by thermal CVD using a low pressure system as noted by Houle et al.
Thermal CVD of copper has previously been reported from other precursors such as CuCl.sub.2 and Cu(C.sub.5 H.sub.7 O.sub.2).sub.2. The copper chloride system requires the addition of hydrogen as a reductant, and operates at temperatures of 400.degree.-1200.degree. C. The products of the reaction are copper and hydrogen chloride, and a reasonable mechanism for this reaction probably involves disassociative chemisorption of both reactants followed by a surface reaction to make HCl which then desorbs. When copper is deposited from copper acetylacetonates, hydrogen is also required in most cases. Generally, the formation of copper from these sources produces poor material of high resistivity.
Another reference generally describing techniques for forming metals on glass surfaces is U.S. Pat. No. 4,321,073 to G. R. Blair. This reference mentioned laser beam dissociation of metal-containing compounds on a glass fiber in order to coat the fiber with the metal. Many classes of organo-transition metal complexes, coordination complexes and metal halides are mentioned in this reference, which is directed to the use of a radiant energy beam to heat the glass substrate in order to dissociate the metal-containing compound.
Other references generally describing the coating of the metal by heating a metal-containing compound include U.S. Pat Nos. 3,438,805; 4,478,890; and 4,574,095. In the first of these, a metal such as copper is coated by heating a metal salt/phosphine complex in the presence of the substrate. The second reference describes the deposition of nickel using a Ni-olefintrifluorophosphine complex which is decomposed. The last of these references describes Cu deposition using Pd seeds where a Pd-containing compound vapor is irradiated with laser light or exposed to a laser-heated substrate in order to reduce the compound vapor to Pd.
While the prior art generally recognizes the desirability of CVD of metals such as copper, the precursors and techniques previously tried have not been successful, for reasons such as those described hereinabove. In particular, these prior techniques require either unrealistically high processing temperatures or produce films that are contaminated with carbon and/or oxygen. The use of chloride precursors in particular has required high processing temperatures while the use of acetylacetonate precursors has led to the deposition of films with high levels of carbon and/or oxygen.
Accordingly, it is a primary object of the present invention to provide an improved technique for CVD of copper and other group IB metals wherein films of high quality can be deposited at low temperatures.
It is another object of this invention to provide improved CVD processes for the deposition of Cu, Ag, and Au films of high quality and good surface morphology.
The low temperature requirement for the deposition of transition metals is most easily met by the decomposition of an organometallic compound. However, for certain metals such as copper, this is made difficult by the instability of organocopper compounds and their tendency to form nonvolatile oligimers and polymers. For example, binary alkyl copper complexes undergo autocatalytic decomposition to alkanes or alkenes and copper metal at temperatures too low for the compounds to have sufficient volatility. This means that very little precursor will arrive at the substrate and large amounts of the reactants will be lost. In the case of binary arylcopper complexes, these materials are more stable but their oligomeric structure lowers their volatility to the point that decomposition occurs before transport. Again, this means that insufficient quantities of reactants will be delivered to the substrate.
It is another object of this invention to provide a class of precursor compounds which can be used in thermal CVD and laser induced CVD processes without the problems described in the previous paragraph.
It is another object of this invention to provide a unique class of precursor compounds which can be utilized in thermal and radiation beam-induced CVD to deposit copper and group IB metals of high quality at low temperatures.
It is another object of this invention to provide a class of improved precursors for thermal and light-induced CVD of Cu, Ag, and Au.
It is a further object of this invention to provide thermal and radiation beam-induced CVD of Cu, Ag, and Au layers on substrates wherein the layers that are deposited exhibit high quality and good surface morphology, and are continuous.
It is another object of this invention to provide an improved technique for the deposition of Cu, Ag, and Au films onto substrates of different shapes, the process providing high quality conformal deposition onto the substrates.
It is another object of this invention to provide an improved thermal and radiation beam-induced CVD process for depositing Cu, Ag, and Au, where the technique is directly applicable to the manufacture and processing of semiconductor devices and structures, being suitable for applications such as chip metallization and repair of conducting lines.
It is another object of this invention to provide an improved technique for thermal and radiation beam-induced CVD of Cu, Ag, and Au where the temperature used in the deposition can be tailored to be sufficiently low that these films can be deposited on substrates whose properties are very temperature-sensitive.